1. Field
Apparatuses consistent with exemplary embodiments relate to a retainer for supporting a photoelectric sensor and a photoelectric pulse wave measuring apparatus including the retainer.
2. Description of the Related Art
Japanese Patent Application Publication No. 2005-040259 discloses a pulse wave measuring apparatus as an example of a photoelectric pulse wave measuring apparatus. The pulse wave measuring apparatus includes a light emitter and a photoelectric sensor. The light emitter includes a light-emitting device that emits, for example, near infrared rays to a blood vessel. The near infrared rays are reflected by the blood vessel. The photoelectric sensor includes a light receiver that receives the reflected light.
The pulse wave measuring apparatus, as described in lines 12 to 27 on page 6 of the Japanese Patent Application Publication, is only used for measuring the number of pulses. Also, because it is lightweight, the number of pulses may be measured during exercise.
The related art has been further developed to a degree that a biomarker can be estimated from a waveform of a pulse wave and the waveform of the pulse wave may be accurately measured. Hereinafter, a description of the development will be described.
FIG. 1 is a schematic drawing of a photoelectric sensor retainer 14 of the related art. The photoelectric sensor retainer 14 includes a pedestal 19 of a photoelectric sensor 75 and a band 90 which is combined with the pedestal 19. The photoelectric sensor 75 is mounted on the pedestal 19. The band 90 may be formed of a resin.
The photoelectric sensor retainer 14 is mounted around a forearm 95. FIG. 1 shows a wrist of the forearm 95. When the band 90 is tightened, the photoelectric sensor 75 contacts a skin surface 96 of the forearm 95.
To precisely measure a pulse wave by using the photoelectric sensor 75 of FIG. 1, a state is provided in which paths of irradiating light and diffusing light do not deviate from each other. This state is maintained for a period of measuring the pulse wave. Accordingly, when the pulse wave is measured, a light emitter 80 and the photoelectric sensor 75 tightly contact the skin surface 96. Also, a pressing force is such a degree that an optic axis of the irradiating light does not deviate.
Therefore, it is desired that a light-receiving surface 77 of the photoelectric sensor 75 is in contact with the skin surface 96 near a radial artery 97 of the forearm 95. The light-receiving surface 77 may face a predetermined measuring direction 74. The predetermined measuring direction 74 may be a parallel direction to a perpendicular line of the skin surface 96.
However, the shape of the skin surface 96 may vary according to age, sex, and physical constitution of a person under examination. Therefore, it is difficult to press the photoelectric sensor 75 near the radial artery 97 in the predetermined measuring direction 74 by simply tightening the band 90.
This is because the tightening of the band 90 cannot control the magnitude and the direction of force that is applied to the photoelectric sensor 75. That is, because the position of the photoelectric sensor 75 on the band 90 is variable, the force provided by the band 90 is dispersed due to the principle of action and reaction.
It can be considered that the above problem may be solved by adding an electrical pressing device after increasing the size of the photoelectric sensor retainer 14 of FIG. 1. However, it is difficult to make the photoelectric sensor retainer 14 lightweight enough to be applied to a portable device.